1. Field of the Invention
The present invention relates to a method for automatically detaching the supporting fabric attached to an element of elastomeric material, generally a length of tread band, in order to maintain its adhesiveness unchanged before it is used in a machine for tyres manufacturing.
Furthermore, the present invention relates to a device designed to automatically detach said supporting fabric; said device eases the task of the operator involved in the operation of detachment and, at the same time, makes it possible for said element to be moved towards a manufacturing drum mounted on the abovementioned machine.
More particularly, the present invention relates to the automatic detachment of the supporting fabric attached to a length of tread band for tyres of the giant type, i.e. for tyres which are suitable to be used on heavy duty vehicles and the like.
2. Description of the Related Art
In the following of the present invention and in the pending claims, the term “elastomeric material” is intended to mean a rubber mixture in its entirety, i.e., containing at least a basic polymer, the reinforcing fillers, as well as further product and process additives normally used for manufacturing and curing a pneumatic tyre.
Tread bands for tyres of the giant type, as described further on in the course of the present description, are normally extruded continuously, because of their sizes and their weight considerably greater than the sizes and weight of the tread bands of car tyres. Thus said tread bands are cut up into pieces of predetermined length, stored in a store and taken therefrom for subsequent feeding to a tyre manufacturing machine.
Said working procedure is substantially used also in the process of tyres manufacturing for cars where, however, it is generally preferred to store the tread band temporarily in the form of a continuous piece on a storage reel together with a supporting fabric which separates the overlapping turns of the elastomeric material from each other, the cutting to length operation of said tread band being performed subsequently, after separation of the supporting fabric, during the stage in which the tread band is delivered to said manufacturing drum.
For greater simplicity of description, reference will be made in the following of the present description to processes for the manufacturing of pneumatic tyres which use lengths of tread band which have been precut to length during their manufacturing stage.
Furthermore, whenever not expressly indicated otherwise, said lengths of tread band are to be understood to be either for tyres of the giant type or for car tyres, without distinction.
In accordance with tyres manufacturing processes known in the art, the operation of removing the supporting fabric from a length of tread band is performed manually by an operator who is responsible, among other tasks, for preparing and positioning said tread band on a suitable feed device placed upstream from a manufacturing drum.
More specifically, lengths of tread band are placed on the supporting planes of a distributor means, generally a moving trolley, positioned close to the aforesaid feed device, and the operator is required to handle each piece separately.
Said pieces are carefully placed on said supporting planes in such a way that the supporting fabric is in contact with the surface of said planes.
Therefore, the operator works on each piece, turning it over a first time so that the supporting fabric is uppermost, and then detaching said fabric in a completely manual way, using only his own strength.
Once the supporting fabric has been removed from the surface of the piece, the successive operations performed by the operator depend on the nature of the process and the manufacturing machine used.
In the case where the abovementioned feed device delivers the tread band in a position above the manufacturing drum, the piece of tread band must be turned over a second time to ensure that it is correctly positioned on the cylindrical surface of the drum.
Once said second overturning movement has been performed the operator has to manually push the tread band up onto said feed device, which is upstream from the manufacturing drum, and which is provided with motor-driven rollers or with a conveyor belt which deliver said tread band to the manufacturing drum.
When, however, said feed device delivers the tread band to a position below the manufacturing drum, the operator does not have to turn said piece over a second time once the supporting fabric has been removed, and merely has to push it towards said feed device.
According to Applicant's perception, manual performance of the abovementioned operations of turning the tread band over and detaching the supporting fabric attached to the latter is particularly onerous for the operator, because of the appreciable weight of the piece, and he is required to make a more than negligible repeated physical effort which is quite harmful to the integrity of the piece that undergoes a plurality of stretching movements and dimensional changes because of the plasticity of the nonvulcanized material, which compromise the quality of the finished product.
In fact, it should be emphasized that in the case of tyres of the giant type, each piece of tread band has a weight which generally varies between 25 and 30 kg.
Furthermore, said physical effort is not only required for turning the piece of tread band over and for detaching the supporting fabric, which must be performed at the same time over the full width of the piece, and progressively in a longitudinal direction along it, but also for conveying said piece, pushed by the operator's force, towards the feed device of the manufacturing drum.
The process of producing a tyre, in particular a tyre of the giant type, makes use of manufacturing machines which, operating according to a predetermined sequence of stages performed partly in a wholly automatic way and partly semiautomatically on two or more manufacturing drums, make it possible to assemble the plurality of semifinished components which make up a finished tyre.
Said semifinished components are represented by: the liner, i.e., a layer which is impermeable to air and which coats the inside of the carcass of a tubeless tyre, the carcass ply, the chafers, the fillers beneath the belt ply, the belt plies (in general, three separate strips of belt ply overlapped by a further strip with circumferential cords), the tread band, and the sidewalls.
The structure and the operation of a manufacturing machine as a whole are not described in the following since they are not relevant to said invention, and any manufacturing machine of the known art may therefore be taken into consideration.
As mentioned above, the tread band represents one of the semifinished products used in the manufacturing process of a tyre, and is produced by an extrusion operation by using a mixture of predetermined formulation which results in the production of a continuous piece of elastomeric material.
Through the use of dies of predetermined cross section, said continuous piece is shaped into a profile which is substantially trapezoidal in transverse cross section.
Thus, the obtained continuous piece of the tread band is subjected to a cooling stage which is conventionally performed by immersing it into a cooling liquid, e.g. water at ambient temperature.
Once said cooling stage is complete, the lower surface of said piece of tread band, that is the surface which constitutes the larger base of the abovementioned trapezoidal cross section and which comes into contact with the abovementioned belt package during manufacturing, is attached to a supporting fabric.
Said fabric performs the function of preserving the adhesiveness of the mixture on the lower surface of the tread band, that is the surface which will come into direct contact with the underlying belt package during the tyre manufacturing process.
In fact it should be emphasized that for reasons relating to the process and the stocks in store, generally the tread band, once it has been produced, is not immediately used but remains stored in the stores for a variable period of time of between few hours and few days.
During said period of time the tread band is inevitably in contact with dust and/or dirt present in the surrounding environment; there is therefore a need to protect its surfaces, in particular to preserve its adhesiveness, by coating it with a supporting fabric.
More particularly, in the case of tread bands for vehicle tyres, a continuous piece of tread band approximately 100 metres long is wound onto a reel together with a suitable fabric, e.g. Meraklon®.
On the other hand, in the case of tread bands for giant tyres the tread band is coated with a supporting fabric which generally consists of a sheet of polyethylene.
The tread band attached to the supporting fabric is then subjected to a cutting to length operation so as to produce pieces of tread band which have predetermined dimensional features for use during the manufacturing stage, said features being suitable for the manufacturing of a particular tyre.
As mentioned above, the cut pieces of the tread band are placed on the supporting planes of a carrying trolley, known in the technical language as “book trolley”, which has the special feature of having the supporting planes all hinged so as to rotate along the same side, i.e. the longer side of said planes, the latter adopting an arrangement similar to that of the pages of a book.
Once it has been loaded, said trolley is brought up close to the manufacturing machine, upstream of a manufacturing drum, where the operator, as indicated above, manually detaches the supporting fabric from the tread band and delivers it to a roller or belt feed device which feeds said manufacturing drum.